Vessel diaphragm and method

ABSTRACT

An elastic thermoplastic diaphragm for use in a vessel having an inner surface. The vessel includes a liner that has an inner liner surface and first and second ends. A first endcap is secured to the liner first end and a second endcap to the liner second end. The diaphragm is secured to the inner vessel surface and seals along a peripheral edge to the vessel inner surface so as to define a volume inside the vessel. The diaphragm can flex, and thereby increase or decrease the volume.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to a diaphragm and more specifically to a thermoplastic diaphragm assembly for use in a pressure vessel.

[0003] 2. Discussion of Related Art

[0004] A water system, for example a well water system, typically includes a pneumatic accumulator tank, a pump, and a water source. In a base form, the pneumatic accumulator tank receives water from the water source. A quantity of air pressurizes the pneumatic accumulator tank. The pneumatic accumulator tank retains the air in the tank and supplies pressurized water to the water supply system. Thus, it is not necessary for the pump to continuously pressurize the water supplied to the tank; the water provided to the water supply system is pressurized by the air in the tank.

[0005] A diaphragm separates the air and water in the pneumatic accumulator tank. A traditional diaphragm includes a bag formed from cup-shaped halves that can either stretch or unfold to receive the air. In such a traditional accumulator tank, the tank itself is formed from a pair of metal shells, and mating ends of the cup-shaped diaphragm halves are clamped between the metal shells to mount the diaphragm to the tank and seal the diaphragm.

[0006] Normally, water is introduced into the diaphragm, and air is introduced into the remaining volume of the tank. Accordingly, a water inlet to the diaphragm is formed in an end wall of the tank. The diaphragm isolates the water from the metal walls of the tank, and thereby prevents corrosion of the tank. However, in the past it has been difficult and expensive to secure the diaphragm within the tank. It has been especially difficult to assembly and seal the water inlet to the diaphragm. Therefore, there exists a need in the art for an improved diaphragm water inlet structure that facilitates assembly and reliably seals the diaphragm water inlet.

[0007] Moreover, the traditional diaphragm assembly is expensive and not adapted for economical use in non-metal tanks, such as thermoplastic composite pressure vessels. Therefore, there exists a need in the art for an improved diaphragm assembly that is adapted for use in thermoplastic pressure vessels.

SUMMARY OF THE INVENTION

[0008] The present invention is directed toward an improved diaphragm water inlet structure that facilitates assembly and sealing of the diaphragm to the pressure vessel. The present invention is further directed toward an improved thermoplastic diaphragm that is adapted for use in a thermoplastic composite pressure vessel.

[0009] In accordance with one embodiment of the present invention, a first diaphragm is bowl-shaped and has an open end that is surrounded by a peripheral edge. The peripheral edge is sealed to an inner surface of the pressure vessel and defines an enclosed space for receipt of fluid, such as water. The diaphragm and pressure vessel are formed of compatible thermoplastic material to permit sealing or heat welding of the diaphragm to the pressure vessel.

[0010] In further accordance with the present invention, the pressure vessel includes a cylindrical liner having end caps secured to first and second ends thereof. The liner is preferably formed from a thermoplastic material and may be formed by known techniques, such as extrusion, injection molding, and the like. The end caps are preferably formed from a composite material including a first or inner layer of thermoplastic and a second or outer reinforced layer, which preferably comprises of intermixed thermoplastic and glass fiber materials.

[0011] In further accordance with the present invention, the diaphragm may be sealed to the liner, one of the end caps, or may be sealed between a junction of the liner and one of the end caps. The diaphragm peripheral edge may include a sealing ring to facilitate sealing and securing of the diaphragm to the liner or end cap. Alternatively, the diaphragm may be directly secured to the liner or end cap.

[0012] In further accordance with the present invention, the diaphragm includes first and second cup-shaped diaphragm portions. The first and second diaphragm portions are sealingly secured to one another at their open ends. At least one of the first and second diaphragm portions is sealing secured to at least one of the vessel end caps or the vessel liner, as described hereinbefore.

[0013] The first diaphragm portion extends into the tank and away from one end cap and expands and contracts in use. The second diaphragm portion overlies the one end cap and is relatively stationary in use. An inlet to the diaphragm is formed in the one end cap and the second diaphragm portion by means of which fluid may be introduced into the diaphragm. The second diaphragm portion is stationary in use, and may be formed from a relatively stiffer material than the elastic first diaphragm portion.

[0014] In further accordance with the present invention, an inlet assembly is provided to seal the diaphragm inlet and sealingly secure the diaphragm to the end cap. The inlet assembly includes a seat and a fitting, and the diaphragm includes a sealing ring. The end cap, seat, and the sealing ring each define coaxial or aligned apertures, and the fitting extends through the apertures. The seat and the fitting cooperate to define a ring-shaped groove that sealing captures the sealing ring.

[0015] In further accordance with the present invention, a fitting is formed from a thermoplastic material and is welded or heat-sealed to the endcap at the water inlet to seal the fitting to the water inlet. The fitting may also be welded or heat-sealed to the diaphragm so as to seal the fitting to the diaphragm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] These and further features of the invention will be apparent with reference to the following description and drawings, wherein:

[0017]FIG. 1 is a cross-sectional side view of an apparatus according to a first embodiment of the invention;

[0018]FIG. 2 is a cross-sectional side view of an apparatus according to a second embodiment of the invention;

[0019]FIG. 3 is a cross-sectional side view of an apparatus according to a third embodiment of the invention;

[0020]FIG. 4 is a cross-sectional schematic side view of part of the apparatus shown in FIG. 3;

[0021]FIG. 5 a cross-sectional schematic side view of part of the apparatus shown in FIG. 3;

[0022]FIG. 6 is a schematic cross-sectional view of a diaphragm subassembly according to the present invention;

[0023]FIG. 7 is a schematic cross-sectional view of a pressure vessel incorporating a diaphragm according to the present invention; and,

[0024]FIG. 8 is an enlarged cross-sectional view of a fitting disposed within a vessel of FIG. 7 incorporating the diaphragm assembly of FIG. 6;

[0025]FIG. 9 is an enlarged cross-sectional view of the fitting used in the vessel of FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] A pressure vessel 100 according to a first embodiment of the present invention is shown in FIG. 1. The vessel 100 includes a cylindrical liner 102, and first and second endcaps 104, 106. The cylindrical liner 102 has an outer surface 110 and an inner surface 114. The liner 102 defines an axis 108 and has opposing ends. The first endcap 104 is secured to a first end of the liner 102, and the second endcap 106 is secured to a second end of the liner 102. The liner 102 cooperates with the end caps to define an interior volume 116 of the vessel 100.

[0027] The liner 102 and endcaps 104, 106 are formed from a thermoplastic material. More specifically, the endcaps 104, 106 are generally identical and include a first, inner layer 104 a, 106 a and a second, outer layer 104 b, 106 b. The first layer 104 a, 106 a is formed from a thermoplastic material, such as polypropylene or polyethylene, while the second layer 104 b, 106 b is formed from a reinforced thermoplastic, such as a commingled glass and thermoplastic material, as will be described more fully hereinafter. The liner 102 is preferably formed from a compatible thermoplastic material, such as polypropylene, to facilitate bonding of the endcaps 102, 104 thereto.

[0028] Although the endcaps 104, 106 are preferably identical to one another and generally dome-shaped, it is contemplated that the endcaps may be frusto-conical or flattened, and that the endcaps need not be alike. Moreover, the endcaps may be of any desired shape or size.

[0029] The endcaps 104, 106 are secured to first and second ends of the liner 102 at respective first and second transition areas 103 a, 103 b. The endcaps 104, 106 are secured to the liner 102 at the transition areas 103 a, 103 b by laser welding, hotplate welding, spin welding, or equivalent techniques known in the art of thermoplastic material joining or fabrication, so as to define an integrated or unitary structure. In a preferred embodiment, the endcap first layer 104 a, 106 a extend axially beyond the endcap second layer 104 b, 106 b, as illustrated, so as to define a stepped open end 136 of the endcap 104, 106 that is welded, preferably by laser welding or infrared welding, to the liner 110. Although laser welding or infrared welding to integrally secure or bond the endcaps 104, 106 to the liner 102 is currently preferred, it is contemplated that alternative methods of attachment, such as spin welding, hot plate welding, solvent welding, etc., may be used without departing from the scope and spirit of the present invention.

[0030] The second layer 104 b, 106 b is preferably a thermoplastic and oriented or non-oriented glass fiber composite layer. Preferably, the second layer 104 b, 106 b is formed from a commingled thermoplastic and glass fiber fabric sold as TWINTEX, commercially available from Saint-Gobain Vetrotex America Inc. (Valley Forge, Pa.). In this embodiment, the glass fibers are woven and in the form of a fabric mat, and in alternative embodiments, the oriented fibers are biaxial, triaxial, looped, and/or stitched. In the preferred and illustrated embodiment, the first and second layers of the endcap 104, 106 are integrally secured to one another, such as by insert molding or compression molding, so as to define a unitary or integral endcap structure.

[0031] An overwrap layer 109 is wound onto the liner 102 and over the transition areas 103 a, 103 b so as to extend over edges of the first and second endcaps 104, 106 adjacent the liner 102. The overwrap layer 109 is a continuous glass filament thermoplastic composite layer (i.e., commingled glass and thermoplastic fibers) that is heat sealed to the liner 102. These fibers are like the TWINTEX fibers that form the endcap second layers 104 b, 106 b, but are supplied in an endless or continuous format suitable for continuous filament winding. As noted hereinbefore, portions of the overwrap layer 109 preferably extend across the transition areas 103 a, 103 b and, accordingly, extend over a portion of the endcaps and overlie at least the free edges of the endcaps 104, 106. Insofar as the endcaps include the reinforced second layers 104 b, 106 b, it is not considered necessary to wrap the overwrap layer 109 completely around the endcaps 104, 106.

[0032] While in the preferred embodiment the overlap layer extends circumferentially around the liner 102 and the transition areas 103 a, 103 b, it is contemplated that the overwrap layer 109 may, instead, be helically wrapped around the liner 102 and the endcaps 104, 106. Further, it is contemplated that the endcaps 104, 106 only include the first layer (i.e., the non-reinforced thermoplastic layer 104 a, 106 a) and that reinforcement of the liner 102 and the endcaps 104, 106 be provided by the helically-wound glass and thermoplastic overwrap layer 109. This later alternative is illustrated in FIG. 3 and discussed hereinafter.

[0033] Moreover, in alternative embodiments described hereinafter, the cylindrical liner 102 and endcaps 104, 106 are thermoset plastic or metal, for example stainless steel or aluminum.

[0034] The vessel 100 receives a diaphragm that is formed from first and second thermoplastic diaphragm portions 120, 122. The first diaphragm portion 120 is generally bowl or cup-shaped, and is formed from an elastomeric thermoplastic material. The term elastomeric thermoplastic material, as used herein, may be any thermoplastic elastomer (TPE), which refers to a diverse group of rubber-like materials including ethyl vinyl acetate (EVA), rubber, rubber blends, polypropylene-rubber blends, as well as materials such as those sold under the trademarks SANTOPRENE and TREFSIN by Advanced Elastomer Systems, Inc. A peripheral edge surrounds an open end of the first diaphragm portion 120, and is integrally connected to a ring 128. Preferably, at least one of the first diaphragm portion 120 and the ring 128 is formed from an elastomeric thermoplastic material that is compatible with the liner material so as to be easily joined to the liner 102 or first endcap inner layer 104 a by the thermoplastic attachment techniques described hereinbefore. Moreover, the first diaphragm portion 120 and the ring 128 are integral with one another so as to define a unitary structure. Naturally, the first diaphragm portion 120 and the ring 128 may be formed at the same time, or may be manufactured separately and then joined to one another by the aforementioned thermoplastic welding techniques.

[0035] The ring 128 is disposed between the peripheral edge of the first diaphragm portion 120 and an inner surface of the first endcap 104, and is joined or sealingly secured to the first endcap 104 at a first joint 134. Preferably, the first joint 134 is disposed at about the end of the liner 102 to about the stepped open end 136 of the first layer 104 a of the first endcap 104, which is generally at the transition area 103 b.

[0036] The second diaphragm portion 122 is also generally bowl-shaped and formed from a thermoplastic material. The second diaphragm portion 122, however, generally conforms to the shape of the inner surface of the first endcap 104 over which it extends. The first and second diaphragm portions 120, 122 are sealed to one another at their open ends. In the preferred and illustrated embodiment the first and second diaphragm portions 120, 122 are in abutting engagement with one another. More specifically, the annular open end of the second diaphragm portion 122 is in sealing engagement with the ring 128 and the annular open end of the first diaphragm portion 120. Naturally, it is considered apparent that the free ends of the diaphragm portions 120, 122 may overlap, or that the ring 128 may be secured to peripheral edges of both the first and second diaphragm portions (i.e., between the inner surface of the second diaphragm portion 122 and the outer surface of the first diaphragm portion 120). Accordingly, the first and second diaphragm portions 120, 122 cooperate with one another to form a bag-like, elastically extendable receptacle separating the interior volume 116 of the vessel 102 into a first or diaphragm cavity 140 a and a second cavity 140 b.

[0037] The diaphragm cavity 140 a defines a volume that can be varied. For example, the diaphragm cavity 140 a has a reduced volume when the first diaphragm portion 120 is in a collapsed condition, compared to an increased volume of the diaphragm cavity 140 a when the first diaphragm portion 120 is in an elastically extended or inflated condition. Due to its location adjacent the first endcap 104, the second diaphragm portion 122 will be generally stationary during extension and retraction of the first diaphragm portion 120.

[0038] An inlet passageway 144 is formed through the first endcap 104 and the second diaphragm portion 122 through which water may be introduced into the diaphragm cavity 140 a. In use, and as described more fully hereinafter, an inlet fitting is disposed through the inlet passageway 144 so as to communicate fluid into and out of the diaphragm.

[0039] The second endcap 106 is semi-hemispherical and dome-shaped, and defines an aperture 160 through which an air valve assembly 162 extends. The air valve assembly 162 is conventional in the pressure vessel art, and will not be discussed further hereinafter.

[0040] In use, the second cavity 140 b is charged or pressurized to a predetermined pressure P1 by use of the valve assembly 162. Water is pumped into the diaphragm cavity 140 a via the inlet 144 and stored in the diaphragm at a pressure P2, which is generally equal to the second cavity pressure P1. When water is required by the water supply system, pressurized water flows from the diaphragm through the inlet 144 and an associated inlet/outlet valve (not shown), to the water supply system. As water flows out of the diaphragm, the diaphragm collapses and the pressures P1, P2 decrease. When the pressures P1, P2 reach a predetermined lower limit, the pump is actuated to introduce further water into the diaphragm cavity 140 a. When the pressures again return to a desired upper limit, the pump is deactivated.

[0041] In the above-described embodiment, the second diaphragm portion 122 isolates fluid from the first endcap 104. Because the second diaphragm portion 122 is adjacent to and coextensive with the inner layer 104 a of the first endcap 104, it does not move or expand in response to the addition of the fluid to the diaphragm cavity 140 a. Accordingly, the second diaphragm portion 122 may be formed of a relatively more rigid, and less expensive, material than the elastically expandable first diaphragm portion 120, if desired. Moreover, since the first endcap 104, and more specifically, the inner layer 104 a of the first endcap 104, is formed from a water compatible thermoplastic material, the second diaphragm portion 122 may be omitted, and the resulting diaphragm would only be formed from the extensible or elastic first diaphragm portion 120. Such an assembly would reduce costs and provide for more efficient assembly and manufacture.

[0042] When manufacturing the vessel 100 depicted in FIG. 1, the liner 110 and endcaps 104, 106 are separately formed. Thereafter, the diaphragm portions 120, 122 are installed in the first endcap 104. Preferably, after the diaphragm portions 120, 122 are properly disposed relative to the first endcap 104, the ring 128, which is held temporarily in place by a friction or interference-type fit, is sealingly secured to the first endcap 104 by heat welding, laser welding, or other equivalent techniques, with laser welding being the currently preferred method. Thereafter, the first endcap 104 with the diaphragm assembly attached thereto, is sealing attached to the liner 102, and the second end cap 106 is secured to the opposite end of the liner 102. As noted previously, the first and second endcaps 104, 106 may be sealingly secured to the liner 102 by conventional thermoplastic joining techniques such as spin welding, hot plate welding, laser welding, infrared welding, or the like, with laser welding and infrared welding being the currently preferred methods.

[0043] Another vessel 200 according to the present invention is shown in FIG. 2. The vessel 200 has many parts that are substantially the same as the vessel 100; this is indicated by the use of the same reference numerals in FIGS. 1 and 2. The apparatus 200 differs primarily in that it includes an alternative elastic thermoplastic diaphragm 250.

[0044] The diaphragm 250 is a semi-hemispherical and dome-shaped or bowl-shaped membrane that has a peripheral edge 252 surrounding its open end. The peripheral edge 252 is secured to the inner surface 114 of the liner 102 at a location intermediate the first and second endcaps 104, 106. The diaphragm edge 252 is sealed to the liner inner surface 252, preferably by heat sealing, or laser, infrared hot-plate or spin welding. The peripheral edge 252 may be slightly built up or enlarged relative to the remaining portions of the diaphragm 250 to facilitate sealing and secure attachment thereof to the liner 102. Alternatively, the diaphragm 250 may include a peripheral ring, similar to ring 128 described hereinbefore, if desired. The diaphragm 250 cooperates with the first endcap 104 and a portion of the inner surface 114 to define a diaphragm cavity 280 that receives water via the opening or inlet 144.

[0045] In accordance with the second embodiment, the diaphragm 250 is secured to the liner 102 at a predetermined position between the liner ends. Thereafter, the endcaps 104, 106 are secured to the liner 102, as described hereinbefore, and the liner 102 and transition areas 103 a, 103 b are wrapped with the overwrap layer 109. Operation or use of the vessel illustrated in FIG. 2 is substantially identical to that of the vessel of FIG. 1, and will not be described further hereinafter.

[0046] With reference to FIGS. 3-5, a vessel 300 comprising a third embodiment of the invention is shown. The vessel 300 has many parts that are substantially the same as the previously described vessels 100, 200; this is indicated by the use of the same reference numerals in FIGS. 3-5 as were used in FIGS. 1 and 2. The vessel 300 has a first end 302 and a second end 304, and includes a liner 102, first and second endcaps 104′, 106′, a helical overwrap layer 319, and a diaphragm assembly 310. The diaphragm assembly 310 is formed from an elastomeric thermoplastic material, such as described hereinbefore.

[0047] The first endcap 104′ is attached at the liner 102 so as to define a first end 302 of the vessel 300, and has a first aperture 326 formed therein for receipt of an inlet assembly. The second endcap 106′ is attached to the liner 102 so as to define the second end 304 of the vessel 300, and has a second aperture 328 formed therein for receipt of a valve assembly. The illustrated first and second endcaps 104′, 106′ each-have only a single non-reinforced thermoplastic dome-shaped thermoplastic layer, similar to the first, inner layer 104 a, 106 a described hereinbefore. The reinforcement or strength of the vessel 300 is primarily provided by the overwrap layer 319 that extends over the liner 102 and around the endcaps 104′, 106′. The overwrap layer 319 is formed from a commingled glass and thermoplastic layer, as described hereinbefore with regard to the overwrap layer 119 of FIGS. 1-2.

[0048] The diaphragm assembly 310 includes a first diaphragm portion 336 and a second diaphragm portion 338. The first and second diaphragm portions 336, 338 are bowl-shaped and have free ends adjacent to the liner 102 and in continuous contact with each other so as to form a seam 340. A sealing ring 342 clamps the free ends of the diaphragms 336, 338 to seal the diaphragms together at the seam 340. The free ends are somewhat enlarged and are captured by a sealing ring 342, which is preferably formed from a thermoplastic material so as to facilitate welding or attachment of the ring 342 to the diaphragm portions 336, 338, if desired. Alternatively, the free ends of the first and second diaphragm portions 336, 338 may be integrally sealed or fused to one another using the techniques described hereinbefore. The first diaphragm portion 336 has an annular sealing rib or O-ring 344 that defines an aperture 346 aligned with the aperture in the first endcap 104′.

[0049] With particular reference to FIG. 4, the inlet assembly 350 at the first end 302 of the vessel 300 includes a ring-shaped seat 354 and a fitting 356. The fitting assembly 356 is adapted to receive an outlet fitting 358.

[0050] The ring-shaped seat 354 is integrally formed in the first endcap 104′ and radially surrounds the endcap aperture. Preferably, the seat 354 is insert molded in the first endcap 104′. The ring-shaped seat 354 includes a radially inwardly facing surface 360 that is aligned with the ring aperture 346 and defines a portion of the first endcap aperture. The seat 354 includes a radially extending flange 364 that is encapsulated in or surrounded by the first endcap 104′. The flange 364 includes projecting ridges that facilitate bonding or integrating of the flange 364 with the first endcap 104′ during molding thereof. As illustrated, portions of the first endcap 104′ extend over each side of the flange 364, thus sandwiching or encapsulating the flange 364 within the endcap 104′, as illustrated. The seat 354 further defines a first ring-shaped groove that surrounds the first endcap aperture and is open to the interior of the vessel 300.

[0051] The fitting 356 has a radially flared proximal end 372 that is received within the vessel 300, and a substantially tubular second portion that extends through the first seat aperture 360. The second portion includes a threaded distal end 370 that is disposed outside the vessel 300.

[0052] The flared first end 372 of the fitting 356 cooperates with the ring-shaped groove of the seat portion 354 to define an annular recess that is adapted to the annular sealing rib 344 of the diaphragm assembly 310. The seat portion 354 and the flared portion 372 cooperate with each other to clamp the ring 344 in the annular recess and to thereby seal the diaphragm assembly 310 to the fitting assembly 350.

[0053] The tubular second portion of the fitting 356 has an annular groove 374 formed therein, as illustrated. The ring-shaped groove 374 receives a C-shaped spring clip 376, while the threaded portion 370 is adapted to receive the outlet fitting or pipe 358.

[0054] During assembly, the diaphragm first portion 336 is placed adjacent the first endcap 104′, and the fitting 356 is pushed through the aligned openings in the first diaphragm portion 336 and the first endcap 104′. The annular sealing rib 344 is trapped in the annular recess formed between the fitting 356 and the seat portion 354, and the spring clip 376 is installed in the groove 374 to retain the fitting 356 in place on the first endcap 104′ and thereby prevents the fitting 356 from being pulled back into the vessel. Thereafter, the first endcap 104′ may be attached to the liner 102, as described hereinbefore, and then the second diaphragm portion 338 is sealing secured to the first diaphragm portion 336. Subsequently, the second endcap 106′ is attached to the liner 102 such as by spin welding or laser welding, as described hereinbefore. The second endcap 324 preferably includes an air valve assembly. Thereafter, the liner 102 and endcaps 104′, 106′ may be helically wrapped with the overwrap layer 319 (i.e., commingled glass and thermoplastic), as described hereinbefore. Alternatively, the endcaps may include a reinforcing outer layer, and only the liner and transition areas may be circumferentially wrapped with the overwrap layer, as discussed previously.

[0055] With particular reference to FIG. 5, a second endcap 106′ at the second end 304 of the vessel 300 is shown to include a second ring-shaped seat 384 and a valve 386. The second ring-shaped seat 384 is substantially identical to the first ring-shaped seat 354, but has been machined in a different manner to facilitate attachment of the valve 386. More specifically, the second ring-shaped seat 384 differs in that it includes a raised central seat 390 that is centered on the axis 320 and defines a valve aperture 392. The valve 386 extends through the valve aperture 392 and seals against the raised central seat 390.

[0056] According to the present invention, prior to the assembly of the vessel 300, the endcaps 104′, 106′ are identical, and integrally include the seats 354, 384. At this point the seats 354, 384 have a solid or continuous central portion. Endcaps that are to be used as first endcaps 104′, as described hereinbefore, are machined so as to form the first aperture 360 while endcaps that are to be used as second endcaps 106′ have a smaller opening, which becomes the valve aperture 392, drilled therein. Otherwise, the first and second endcaps 104′, 106′ are preferably identical.

[0057] As briefly mentioned hereinbefore, during assembly of the vessel 300, the first endcap 104′ with the encapsulated seat 354 provided therein is provided. The seat 354 is machined so as to define the first seat aperture 360, which is sized to accommodate the fitting 356. The fitting 356 is inserted through both the ring aperture in the first diaphragm 336 and the first seat aperture 360 in the first endcap 104′. The sealing ring 344 of the first diaphragm 336 is thus disposed in the annular recess defined by the ring-shaped grooves in the seat 354 and the fitting 356.

[0058] The spring ring 376 is snapped into the groove 374 to hold the fitting 356 in place. The second diaphragm 338 then is aligned with the first diaphragm 336 so that the free ends of the diaphragms 336, 338 are in continuous contact with each other to define the seam 340. The ring 342 clamps the diaphragm free ends so as to seal the diaphragms 336, 338 together at the seam 340. The ring 342, liner 102, and first endcap 104′ are secured to one another using thermoplastic welding or attachment techniques described hereinbefore, preferably laser welding. In this regard it is noted that laser welding can take place on the interior and exterior sides of the vessel subassembly as the second endcap 106′ has yet to be attached to the liner 102.

[0059] At the same or different time the fitting 356 is attached to the first endcap 104′ by laser welding, vibration welding, or the like. Accordingly, the fitting 356 is sealingly secured to the first endcap 104′ and the seat 354 so as to prevent leakage of fluid between the fitting 356, the seat 354, and the first endcap 104′. Following integrating of the fitting 356 with the first endcap 104′ and seat 354, the snap ring 376 may be removed from the fitting 356.

[0060] The second endcap 106′, with the valve 386 extending through the encapsulated seat 354, is attached to the second end of the liner 102 in the same manner as the first endcap 322. The overwrap layer 119 is helically wound around the liner 102 and the endcaps 104′, 106′, as described hereinbefore. During use, the fitting or pipe 358 is secured to the threaded portion 370 of the fitting 356, and fluid is pumped into the diaphragm and withdrawn from the diaphragm via the fitting 356 and the pipe 358. Pressurizing air is injected into the vessel 300 through the valve 386.

[0061] Although the inlet assembly described hereinbefore with reference to FIGS. 3 and 5 has been illustrated as being used in conjunction with a thermoplastic composite pressure vessel, it is considered apparent that it could be used with equal functionality in a metal pressure vessel. For example, in a metal pressure vessel having a first and second dome-shaped end, a first dome shaped end could have a metal sealing ring welded to the first metal tank dome at a location surrounding an inlet opening. Such a sealing ring would be substantially identical in function to the seat 354, and would include an annular groove to receive the annular rib 344 of the diaphragm and a body portion extending through the opening in the tank dome. For a metal tank assembly, the fitting 356 could be integrally secured to the diaphragm adjacent to the annular rib 344, such as by laser or vibration welding, but would otherwise be identical to that described hereinbefore.

[0062] With reference to FIG. 6, a thermoplastic diaphragm assembly 400 according to the present invention is illustrated. The diaphragm assembly 400 includes a first diaphragm portion 402, a second diaphragm portion 404, and a fitting 408. The first and second diaphragm portions 402, 404 include open ends 402 a, 404 a that are overlapped and secured to one another by any of the techniques described hereinbefore so as to form an overlapping joint 406. The first diaphragm portion 402 defines an opening through which the fitting 408 sealingly extends, as illustrated. The placement and attachment of the fitting within the diaphragm assembly is described hereinafter. However, it is noted that, with the thermoplastic diaphragm assembly 400 it is possible to manufacture a diaphragm subassembly that is essentially complete and adapted for placement in a pressure vessel as a unitary structure.

[0063] Moreover, with the diaphragm assembly 400 it is preferred that, since only the second diaphragm portion 404 will be required to extend/collapse during use, the first diaphragm portion 402 will be formed from a relatively less flexible material than that of the second diaphragm portion 404. Forming the first diaphragm portion 402 from a relatively stiff or non-elastic material reduces the material costs for the diaphragm assembly 400.

[0064] The first diaphragm portion 402 includes a screen 403 and an annular seat 405. The screen 403, which may be integrally formed with the first diaphragm portion 402 or secured thereto, overlies the fitting 408 and the port defined thereby. The screen 403 has a series of apertures formed therein and prevents the second diaphragm portion 404 from being pulled through the fitting 408 during collapse of the second diaphragm portion 404.

[0065] With reference to FIG. 7, a thermoplastic pressure vessel 500 according to the present invention is illustrated. Insofar as several of the components of this pressure vessel 500 are identical to those described hereinbefore with reference to FIG. 3, those portions are identified with identical reference numbers as used in FIG. 3, and will not be described in detail hereinafter.

[0066] The pressure vessel 500 includes first and second endcaps 104′, 106′, a liner 102, a helical overwrap layer 319, a diaphragm consisting of the second diaphragm portion 404 (FIG. 6), and a fitting 408. The endcaps 104′, 106′ are secured to ends of the liner 102, and the overwrap layer 319 is helically wrapped around the liner and endcaps. The fitting 408 extends through an opening in the first endcap 104′. The air valve is received in the second endcap 106′, as described hereinbefore with regard to FIG. 5. The second diaphragm portion 404 is secured to the liner 102 at a location between the first and second endcaps 104′, 106′. Naturally, the diaphragm may be like that illustrated in FIG. 6 so as to include both first and second diaphragm portions 402, 404.

[0067]FIG. 9 illustrates attachment of the fitting 408 to the first endcap 104′ in the pressure vessel 500 shown in FIG. 7. FIG. 8, to be described hereinafter, illustrates attachment of the fitting 408 to the first endcap 104′ when the diaphragm assembly is generally as shown in FIG. 6.

[0068] With referenced to FIG. 9, the fitting 408 includes radially extending flange 410, an inner tubular sidewall 412, and an outer tubular sidewall 416. The flange 410 extends from one end of the inner tubular sidewall 412, while the outer tubular sidewall 416 extends from the opposite end of the inner tubular sidewall 412. An annular notch or groove 414 is formed in the outer surface of the inner tubular sidewall 412 for receipt of an optional O-ring. A stepped surface 418 is provided at the union of the inner and outer tubular sidewalls 412, 416, and serves to assist in securing the fitting 408 to the endcap 104′, as will be described hereinafter.

[0069] The first endcap 104′ has the ring shaped seat 454 insert molded therein, as noted hereinbefore. The ring shaped seat includes an annular wall 458 has an annular or radial inner surface in face to face contact with the outer surface of the fitting inner tubular sidewall 412 and an end face 455 in abutting contact with the fitting flange 410, as illustrated. Further, the endcap 104; has an upstanding wall 104 a′ coaxial with the annular wall 458 of the ring shaped seat 454. The upstanding wall 104 a′ has a radially inwardly facing surface that is in face-to-face contact with the outer surface of the inner tubular sidewall 412. As such, the fitting 408 is in substantially continuous contact with the endcap 104′ and the seat 454 along the length of the inner tubular sidewall 412 and a portion of the flange 410. Accordingly, when the fitting 408 is secured to the endcap 104′, such as by vibration welding or other compatible techniques, a large bonding area extending from the upstanding wall 1.04 a′ of the endcap 104′ to the end face 455 of the annular wall 458 is provided. Moreover, since the bonding or sealing surface extends outwardly over the upstanding wall 104 a′ and, therefore, relatively beyond the seat 454, even if the bonding between the seat 454 and the first endcap 104′ fails, the vessel will still not leak due to the sealing of the fitting 408 to the endcap 104′ outboard of the seat.

[0070] Moreover the stepped portion 418 is useful in securing the fitting 408 to the endcap 104′. Since the stepped portion 418 is adjacent to the annular end face of the upstanding wall 104 a′ of the first endcap 104′, application of heat and pressure to the stepped portion 418 will upset or stake the stepped portion, and thereby cause the stepped portion 418 to flow onto and bond with the annular end face of the upstanding wall 104 a′. This situation is illustrated in phantom in FIG. 9 and indicated with the reference numeral 418′. Accordingly, the fitting 408 will be clamped on the endcap 104′ by cooperation of the upset stepped portion 418′ and the flange 410.

[0071] The fitting 408 is formed from a thermoplastic material that is compatible with the endcap 104′ and the seat 454 so as to facilitate bonding or welding of the fitting thereto, preferably by vibration welding or laser welding. The fitting 408 may be formed from a reinforced thermoplastic material, such as a glass reinforced thermoplastic. Preferably, the attachment or welding of the fitting 408 occurs substantially continuously along the inner tubular portion 412, the radially inwardly facing portion of the seat 454, and the annular end wall 455 of the seat 454, as described hereinbefore.

[0072]FIG. 8 illustrates attachment of the fitting 408 to a vessel including the diaphragm assembly illustrated in FIG. 6. Accordingly, FIG. 8 differs from FIG. 9 in that the seat 405 provided by the first diaphragm portion 402 is secured to an inwardly facing surface of the flange 410 and, thus, the flange 410 is captured between the end wall 455 and the diaphragm seat 405. The screen 403 is spaced a short distance from the fitting 408. Accordingly, the fitting flange 410 is preferably secured, by the aforementioned techniques, to the first diaphragm portion seat 405 to form a subassembly consisting of the first diaphragm portion 402 and the fitting 408 and, optionally, the second diaphragm portion 404. The subassembly may be installed in the first endcap 104′ and secured thereto by welding the fitting to the end wall 455 and the upstanding wall 104 a′, as described hereinbefore with regard to FIG. 9. It is believed that the illustrated structure has essentially been described hereinbefore, and will be readily appreciated by those skilled in the art.

[0073] The embodiments described herein are examples of structures, systems and methods having elements corresponding to the elements of the invention recited in the claims. This written description may enable those skilled in the art to make and use embodiments having alternative elements that likewise correspond to the elements of the invention recited in the claims. The intended scope of the invention thus includes other structures, systems and methods that do not differ from the literal language of the claims, and further includes other structures, systems and methods with insubstantial differences from the literal language of the claims. 

What is claimed is:
 1. A thermoplastic diaphragm for use in a vessel having an inner surface, said diaphragm comprises a peripheral edge, and is adapted to be sealed along said peripheral edge to said vessel inner surface so as to define a volume inside said vessel, said diaphragm is operable to expand and collapse so as to increase or decrease said volume.
 2. The diaphragm as defined in claim 1, wherein said diaphragm continuously seals along said peripheral edge so as to isolate, a first fluid portion from a second fluid portion.
 3. The diaphragm as defined in claim 1, further comprising an annular ring having inner and outer sides and being disposed between said peripheral edge and said vessel inner surface, said peripheral edge seals to said inner side of said ring and said vessel inner surface seals to said outer side of said ring, whereby said diaphragm is sealed to said vessel inner surface at said peripheral edge.
 4. The diaphragm as defined in claim 1, wherein the diaphragm is formed from a thermoplastic elastomeric material.
 5. The diaphragm as defined in claim 4, wherein the thermoplastic elastomeric material is selected from the group consisting of ethyl vinyl acetate, rubber, rubber blends, and polypropylene-rubber blends.
 6. A vessel subassembly, comprising: a thermoplastic cylindrical liner having a first and second ends; a first thermoplastic endcap secured to said liner first end; a second thermoplastic endcap secured to said liner second end, said liner and said first and second endcaps cooperating to define an interior volume of said vessel subassembly; and a thermoplastic diaphragm, said diaphragm being sealed an inner surface of one of said liner and said first and second endcaps so as to separate said interior volume into first and second chambers.
 7. The vessel as defined in claim 6, wherein said diaphragm includes a peripheral edge, and said diaphragm is sealed along said peripheral edge to said endcap inner surface.
 8. The vessel as defined in claim 6, wherein said diaphragm includes a first diaphragm portion and a second diaphragm portion, said second diaphragm covering said second endcap inner surface.
 9. The vessel as defined in claim 6, wherein said diaphragm includes a peripheral edge that is sealed to an inner surface of said liner.
 10. A method of assembling a vessel having an inner surface, comprising the steps of: providing a liner having first and second ends and an inner surface defining a portion of said vessel inner surface; securing a diaphragm to an inner surface of said vessel; and securing a first endcap to said liner first end and a second endcap to said liner second end, each of said first and second endcaps having an inner surface defining a portion of said vessel inner surface.
 11. The method as defined in claim 10, further comprising the step of securing said diaphragm directly to the inner surface of one of said first or second endcaps.
 12. The method as defined in claim 10, further comprising the step of securing said diaphragm directly to said liner inner surface.
 13. The method as defined in claim 10, wherein said diaphragm comprises a ring, and wherein said diaphragm securing step includes the steps of securing said diaphragm to said ring, and securing said ring to said vessel inner surface.
 14. The method as defined in claim 13, further comprising the steps of disposing an assembly seam between said endcaps and said liner, and securing said ring to said liner inner surface at a location spaced from said assembly seam.
 15. The method as defined in claim 10, wherein one of said securing steps includes adhesive sealing, heat sealing, hot plate welding, laser welding, vibrational welding, or spin welding.
 16. A vessel, comprising: a cylindrical liner having an end and defining an axis; an endcap attached to the liner end and comprising a ring-shaped seat, the seat defining a seat aperture through the endcap, and the seat having a portion extending radially outward and defining a ring-shaped first groove, the first groove having an open end facing axially in toward the vessel; a thermoplastic diaphragm comprising a sealing ring defining a ring aperture; and a fitting assembly comprising a fitting, the fitting extending through the ring aperture and the seat aperture, and the fitting having a portion extending radially outward and defining a ring-shaped second groove, the second groove having an open end facing axially out away the vessel, the first and the second ring-shaped grooves cooperating with each other to define an annular recess, the ring being disposed in the annular recess, and thereby sealing the diaphragm to the fitting assembly and the ring-shaped seat.
 17. The vessel as defined in claim 16, wherein the fitting further defines a C-ring groove disposed outside of the vessel, and the fitting assembly further comprising a C-ring disposed in the C-ring groove, thereby temporarily securing the fitting to the endcap.
 18. The vessel as defined in claim 16, wherein the fitting assembly further comprises a threaded outer cap, and the fitting has a threaded end threadedly connected to the threaded outer cap.
 19. The vessel as defined in claim 16, wherein the diaphragm is a first one of a plurality of diaphragms and further comprising a second diaphragm and a rib, the first and second diaphragms having free ends in continuous engagement with each other to define a seam, the rib clamping the first and second diaphragms together at the free ends, and thereby sealing the first and second diaphragms to each other at the seam.
 20. The-Vessel as defined in claim 16, wherein the diaphragm is a first one of a plurality of diaphragms and further comprising a second diaphragm, said first and second diaphragms having free ends in continuous engagement and welded to one another and thereby sealing the first and second diaphragms to each other at the seam.
 21. The vessel as defined in claim 16, wherein the endcap is a first one of a plurality of endcaps and further comprising a second endcap attached to a liner end opposite the first endcap, the second endcap comprising a ring-shaped seat with a raised portion, the raised portion defining a valve aperture, and the vessel further comprising a valve extending through the valve aperture that is seated in the raised portion and sealed to the second endcap.
 22. A thermoplastic diaphragm assembly, comprising: a first diaphragm portion, said first diaphragm portion being generally bowl shaped and defining an open end and an inlet opening; a second diaphragm portion, said second diaphragm portion being generally bowl shaped and having an open end, said first diaphragm portion open end being secured to said second diaphragm portion open end, and, a fitting secured to an outer surface of said first diaphragm portion at said inlet opening.
 23. The assembly according to claim 22, wherein at least one of said first and second diaphragm portions is formed from a thermoplastic elastomer material.
 24. The assembly according to claim 22, wherein said first diaphragm portion is relatively less flexible than said second diaphragm portion.
 25. The assembly according to claim 22, wherein said first diaphragm portion includes a screen that overlies said fitting.
 26. The assembly according to claim 25, wherein said screen is integrally formed with said first diaphragm portion. 